Solder joints are used widely throughout the semiconductor arts as a convenient means for forming physical and/or electrical connections between device components. Such components may be, for example, a die and an IC packaging substrate, or an IC packaging substrate and a Printed Circuit Board (PCB). Typically, solder joint formation involves the mechanical or electrochemical deposition of solder onto a bond pad which is disposed on a surface of at least one of the components to be joined together, followed by solder reflow.
FIG. 1 illustrates a typical solder joint 101 formed between a Ball Grid Array (BGA) substrate 103 and a die 105. Such a joint, which is common in flip chip packaging, comprises a portion of solder 107 that spans between a first bond pad 109 disposed on the BGA substrate 103 and a second bond pad 111 disposed on the die 105. In the particular device illustrated, the BGA substrate 103 is equipped with a solder mask 113 that defines the first bond pad 109. Hence, the solder joint formed to the BGA substrate 103 is solder mask-defined (SMD). By contrast, the solder joint formed to the die 105 is non-solder mask-defined (NSMD).
In a typical flip chip device, the die 105 and the BGA substrate 103 will have differing coefficients of thermal expansion. Consequently, varying amounts of stress and strain are applied to the solder joint as the device undergoes thermal cycling. Over time, these forces can cause the solder joint to crack, which may result in mechanical and/or electrical failure of the joint and/or the device.
The issue of solder joint failure and its effect in shortening the lifetime of semiconductor devices that contain solder joints has been recognized in the art for some time. Consequently, a variety of approaches have been proposed in the art to minimize solder joint failure, and to improve the reliability of semiconductor devices employing solder joints. Most of these approaches are undesirable, however, in that they significantly complicate the manufacturing process.
There is thus a need in the art for a simple method for forming solder joints that are more resistant to stress and strain, and that exhibit improved lifetimes. There is also a need in the art for devices made in accordance with such a method. These and other needs may be addressed with the devices and methodologies disclosed herein.